Method and apparatus for fracturing of subsurface formations

ABSTRACT

This is a system for generating a high pressure, e.g., for stimulating by injecting fluid or fracturing, at a selected vertical interval in a subsurface formation penetrated by a well bore. A cylinder member which closely fits the walls of the well bore is inserted into the well bore at the interval to be stimulated. High-pressure fluid is directed through ports in the wall thereof at the center longitudinally of the cylinder to the point of the formation to be fractured. The fluid friction loss in the annular area between the close-fitting cylinder and the bore hole wall permits the high-pressure fluid to be at fracturing or stimulation pressure only at the selected interval.

LCDDUOo atszstovi United States Patent 1 1 3 n 3,825,071 Veatch, Jr. July 23, 1974 .4] METHOD AND APPARATUS FOR 3 ,393,744

FRACTURING OF SUBSURFACE FORMATIONS Inventor: Ralph W. Veatch, Jr., Tulsa, Okla.

Assignee:

Okla.

Filed: Dec. 18, 1972 Appl. No.: 316,173

US. Cl. 166/308, 166/177 References Cited UNITED STATES PATENTS 7/1931 Granger 166/250 X 5/1962 Fast et a1. r. 166/305 R 9/1966 5/1062 Amoco Production Company, Tulsa, 7

7/1968 Fagg et al. 166/187 Primary Examiner-Stephen J. Novosad Attorney, Agent, or Firm-John D. Gassett; Paul F. l-lawley ABSTRACT This is a system for generating a high pressure, e.g., .for stimulating by injecting fluid or fracturing, at a selected vertical interval in a subsurface formation penetrated by a well bore. A cylinder member which closely fits the walls of the well bore is inserted into the well bore at the interval to be stimulated. Highpressure fluid is directed through ports in the wall thereof at the center longitudinally of the cylinder to g the point of the formation to be fractured. The fluid friction loss in the annular area between the closefitting cylinder and the bore hole wall permitsthe high-pressure fluid to be at fracturing or stimulation pressure only at the selected interval.

6 Claims, 2 Drawing Figures PATENTEU JUL2 31974 sum 1 or 2 1 METHOD AND APPARATUS FOR FRACTURING F SUBSURFACE FORMATIONS BACKGROUND'OF. THE INVENTION 1. Field of the Invention This invention relates to a method of treating an underground formation penetrated by a well bore. It relates especially toa method of creating a fracturing pressure-at a vertically isolated interval in the undergroundformation. a

2. Setting of the Invention Many oil and gaswells are drilled into formations that are considered tight, e.g., the formation has low permeability and is reluctant to giveup its fluid. Various treating techniques have been developed. However, the development of the hydraulic fracturing technique, which started in the late I940s, is considered to be the outstanding improvement in obtaining more oil and gas from such low permeability-type reservoirs or, for injecting fluids into them. The hydraulic fracturing technique broadly includes injecting a special-type fracturing fluid into theformation at a rate and under sufficient pressure so as to cause the formation to crack. The hydraulic fracturing fluid may also carry propping agents which are left in these cracks so that the cracks will notclose' when the pressure is relieved. Although the hydraulic fracturing technique has been developed to a high degtee, there still, remains some problem areas; One of these is the creation of a fracture at a selected vertical interval. This can be done in some cases withpresent fracturing techniques, but usually involves the use of several isolating packers. This present invention teaches a novel way of obtaining hydraulic fractures and also shows how the fracture can be isolated to a selected interval. 1 1

There is awealth of literature, including patents, on

forations 44 at the interval in formation 16' at which it that I can inject anyspecial formation treating fluid which I desire by use of this system.

BRIEF DESCRIPTION OF THE DRAWINGS DETAILED DESCRIPTION O THE INVENTION Attention is first directed to FIG. Lwh'ich shows in schematic form the preferred embodiment of-my invention for use with a cased bore hole. I willdiscuss'it in this description'in connection with fracturing a formation, although it can be used in other stimulating techniques. Shown thereon is a well bore having casing 12 and cement 14in the annulus between the casing and the bore hole wall. The bore hole casing and cement extend through a subterranean formation 16. Formation-l6 is typically. a type formation in which it is desired to initiate a fracture so thatoil or gas can be recovered more readily. In this regard, casing 12 has peris desired to create a fracture. A tubing string'18 is suspended from well head. means 21 inthebore hole and hydraulic fracturing. However, none of them, tomy knowledge, show an arrangement whereby pressure is built up at one isolated interval in the well bore by using restricted or limited flow in the well bore away from that point at which it is desired to generate the high pressure. One of the patents which shows packer configuration for fracturing is U.S. Pat. No. 3,385,367; however, the packers shown therein are designed to completely seal with the casing. In my system I obtain fracturing pressures without obtaining a seal.

SUMMARY OF THE INVENTION In a preferred embodiment, a cylinder means closely fitting the well bore in the interval to be fractured is lowered to that interval. The cylinder means has port means in the walls about halfway between the ends which are closed. A passageway extends from the exterior of one end of the cylinder means to the exterior of the other end. Other means are provided for supplying fluid under pressure to the interior of the cylinder means and, thus, through the port means to the interval to be treated. Fluid under sufficient pressure to fracture or otherwise treat the formation is supplied through the port means in the cylinder. The fluid friction loss in the annular space between the'close-fitting cylinder means and the bore hole wall causes a'quick reduction in pressure and the only point in the well bore which is subjected to fracturing or selected treating pressure. is that interval immediately adjacent the port means in the cylinder means. It is to be understood extends to the vicinity of formation16.

My novel device,- which makes a fracturing technique disclosed herein possible,is suspended at the lower end of tubing string 18. This includes an outer cylinder 30 which is closed at the lower end and the upper end by plate means 38 and 40 respectively. Cylinder 30 has-a series of circumferentially spaced perforations or port means 42. The device is lowered such-that port means 42 are positioned adjacent to perforations 44 of casing 12. I wish to avoid a buildup of pressure in the casing below cylinder 30 so I provide a vertical relief or bypass tube. 36 which extends completely through the end members 38 and 40. Tube 36 has upper opening 36A and lower opening 36B which are above and below end means 40 and 38 respectively. Thus, the pressure below plate 38 and aboveend 40 tends to equalize, except for the vertical hydrostatic gradient.

There exists an annulus 34 between cylinder 30 and casing 12. This annulus is rather narrow and is designed so that there will be a large pressure drop from port 42 to the well bore on either end of cylinder 30. There also exists an annulus 28 between tubing '18 and casing 12. This is connected through well head 21 to outlet 24 having valve 26. This permits the release of fluid from the interior of the well. Means are also provided for providing high pressure or treating fluid to tubing 18. This includes an inlet line 20 having valve 22 and which is connected to a treating or high-pressure fluid source not specifically shown. This source can be any well known means such as pump means, tanks, and so forth which can provide any selected fluid to tubing 18.

I shall now discuss the operations of.my device shown in FIG. 1. .As mentioned, 1 lower cylinder member 30 pressure fluid through line 20 from a source not shown.

This fluid is pumped downwardly through tubing 18 out port 42, and then it starts to flow in a restricted manner up annulus 34 to above upper end plate 40, and down through annulus 34 to below lower end member 38. The fluid that flows downwardly returns upwardly through relief tubing 36 so that there is no buildup of fluid or fluid pressurebelow plate 38. During this time, I partially open valve 26 at the surface so that fluid from annulus 28 can flow out. I depend on the high resistance of annulus 34 so that the only place in the well bore, outside of tubing 18 and the interior of cylinder 30 in which the pressure is at fracturing or treating level, is in the immediate vicinity of port 42. I continue pumping high-pressure fluid until the pressure at point 46 is sufficiently high to fracture the formation, causing fracture 48.

Due to the small clearance between the outside of cylinder member 30 and the inside of casing 12, there is a large pressure drop due to high friction loss between port 42 and cylinder 30 and the interior of casing 12 on either end of cylinder 30. In other words, the pressure at the fluid outlet port 42 is much higher than at the extremes of the device. For example, the annulus of between a 5 inch OD cylinder member 30 and a 6 inch ID casing 12, in which the cylinder member 30 is placed, has effectively the same friction drop as a circular pipe having an internal diameter of 125 inches.

At a flow rate of only 30 barrels per minute, the friction drop in the area of the annular space is in theorder of 100 psi per footof annular space length. Thus, if cylinder member 30 is feet long, the pressure drop in the 10 foot long section from the center to each end is in the order of 1,000 psi. Therefore, the pressure at the center of the section, or near port'42, is about 1,000 pounds per square inch higher than in'the annular space within the casing above the tool and in the space below the tool. Thus, I effectively cocentrate my extremely high pressure, which is necessary for fracturing, at port 42. v

.I can also use my system just described for treating the well bore, or the formation 16, with special treating fluids. For example, I can inject any special treating fluid such as acidic fluids; high viscosity fluids such as guar gum gels, cellulose gels; solid suspensions; polymeric fluids for well-known formation treating purposes.

In FIG. 1, hole 10 was lined with casing 12 throughout the entire length and including through the producing formation 16. However, in many cases the casing does not extend completely through the producing formation 16 and the well is said to have an open-hole completion; however, my invention can be used for that. The modificationparticularly suitable for openhole completion is shown in FIG. 2. Shown thereon is casing 52 having a cement sheath 54 surrounding it. Casing 52 is shown as terminating at some point up hole 10A above formation 17. The primary difference between the device of FIG. 2 and FIG, 1 is that I provide on the exterior of cylinder member 30 a plurality of packing elements 56, 56A and 56N on either side of port means 42. I size these so that there is very restricted flow from port 42 through the annulus between the packers and the bore hole wall. To aid me in selecting the proper size packers 56, I use calipers to survey the size of bore hole'lOA through subsurface formation 16. Then I can size my packers 56 through 56N to give me the desired flow resistance between the packers and the bore hole wall. Here an attempt is made to have the packer elements fit as closely as possible to the bore hole wall without sealing. This is accomplished by utilizing either cup-type packer elements or inflatable packer elements which are expanded in an effort to contact, but not seal with, the bore hole wall. However, for this device to operate effectively, it is not necessary to have such a contact. I

While the above invention has been described in detail, it is to be understood that various modifications can be made thereto without departing from the spirit or scope of the invention.

I claim:

1. An apparatus for fracturing an interval of a subsurface formation penetrated by a well bore which comprises: I

a cylinder means closely fitting the well bore in a non-fluid-sealing relationship in the interval to be fractured, said cylinder havingport means through the walls thereof intermediate the ends,

means closing the endsof said cylinder means;

means defining a relief passageway extending from the exterior of one end through said cylinder means to the exterior of the other end thereof; and

means for supplying fluid under pressure to the interior of said cylinder means.

2. An apparatus as defined in claim 1 and including packing elements on the exterior of said cylinder means, said packing elements closely fitting said bore hole in a non-sealing relationship.

3. A method of treating a subsurface formation penetrated by a well bore which comprises:

establishing a first channel from a high-pressure treating fluid source to a surface on said subsurface formation-at which is desired to apply fluid from said source,

establishing a second channel within said well bore from said surface to a first level in said well bore above said surface, said second channel having a high resistance to the flow of fluids therethrough;

establishing a third channel in said well bore from said surface to a second level in said well bore below said surface, said third channel having a high resistance to the flow of fluid therethrough; and establishing a fourth channel between said first level and said second level, said fourth channel having essentially no resistance to the flow of fluids therethrough.

4. A method as defined in claim 3 includes pumping fluid through said first channel at a pressure and rate sufficie-nt to fracture said subsurface formation.

5. A method as defined in claim 3 in which a driving fluid is injected through said first channel into said formation at a pressure below the fracturing pressure of said formation.

6. A method as defined in claim 3 in which a formation-treating fluid is injected through said first channel into said formation at a pressure below the fracturing pressure of said formation. 

1. An apparatus for fracturing an interval of a subsurface formation penetrated by a well bore which comprises: a cylinder means closely fitting the well bore in a non-fluidsealing relationship in the interval to be fractured, said cylinder having port means through the walls thereof intermediate the ends, means closing the ends of said cylinder means; means defining a relief passageway extending from the exterior of one end through said cylinder means to the exterior of the other end thereof; and means for supplying fluid under pressure to the interior of said cylinder means.
 2. An apparatus as defined in claim 1 and including packing elements on the exterior of said cylinder means, said packing elements closely fitting said bore hole in a non-sealing relationship.
 3. A method of treating a subsurface formation penetrated by a well bore which comprises: establishing a first channel from a high-pressure treating fluid source to a surface on said subsurface formation at which is desired to apply fluid from said source; establishing a second channel within said well bore from said surface to a first level in said well bore above said surface, said second channel having a high resistance to the flow of fluids therethrough; establishing a third channel in said well bore from said surface to a second level in said well bore below said surface, said third channel having a high resistance to the flow of fluid therethrough; and establishing a fourth channel between said first level and said second level, said fourth channel having essentially no resistance to the flow of fluids therethrough.
 4. A method as defined in claim 3 includes pumping fluid through said first channel at a pressure and rate sufficient to fracture said subsurface formation.
 5. A method as defined in claim 3 in which a driving fluid is injected through said first channel into said formation at a pressure below the fracturing pressure of said formation.
 6. A method as defined in claim 3 in which a formation-treating fluid is injected through said first channel into said formation at a pressure below the fracturing pressure of said formation. 